Description of problem:
To get n monitors emulated in the guest currently required n pci qxl devices.
This has several problems:
needless waste of memory.
hard to support for linux guests (Xinerama required, Xrandr doesn't allow
different cards)
See planned qemu support in bug #770842.
Suggested solution:
Perhaps using the "heads" property to specify the number of monitors?

Talking to Alon on #spice last week, I learnt that there is not actually any host visible configuration required in order to support multiple monitor mode with QXL. It is all negotiated directly between the SPICE client and the guest QXL driver. So I'm not sure there's any work to be done in libvirtd itself afterall.

Sounds good. But maybe there is a initial configuration that might be exposed? I mean the 'heads' parameter should mean how many monitors will be 'connected' at start (something like the proposed -global qxl-vga.num_displays=2 or similar).
I think that if this is supported than we should modify the behavior in this way as well.

Martin,
The way this was designed there is no need to involve the host in the number of monitors - and conversely there is no way for the host to request a limitation to the number of monitors. Practically the number of monitors will be limited by either the guest actions directly (xrandr / gnome-control-center) or by client triggered (initial MonitorsConfig sent when client connects).
So there is no need or meaning to have a heads parameter.
If you would say what you are trying to accomplish it would be possible to discuss a fix for it.
Alon

(In reply to comment #5)
I was just trying to clarify if anything is needed and you basically answered my question, so from my point of view this could be closed as NOTABUG.
What is your opinion, Oved?

(In reply to comment #6)
> I was just trying to clarify if anything is needed and you basically
> answered my question, so from my point of view this could be closed as
> NOTABUG.
That seems correct to me, so I'm closing as NOTABUG, but if I'm wrong about that of course reopen.